U.S. patent application number 13/232007 was filed with the patent office on 2012-05-03 for image forming apparatus.
This patent application is currently assigned to BROTHER KOGYO KABUSHIKI KAISHA. Invention is credited to Taizo MATSUURA.
Application Number | 20120107017 13/232007 |
Document ID | / |
Family ID | 45996935 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120107017 |
Kind Code |
A1 |
MATSUURA; Taizo |
May 3, 2012 |
Image Forming Apparatus
Abstract
An image forming apparatus includes: a photosensitive drum
configured to rotate about a rotational axis extending in an axial
direction; and a charger that charges the photosensitive drum. The
charger includes: a wire electrode; a grid electrode having a grid
surface that faces the photosensitive drum between the wire
electrode and the photosensitive drum; and a pair of shield
electrodes, which faces each other with interposing the wire
electrode therebetween, and which extends in a substantially
orthogonal direction to the grid electrode. The grid surface is
inclined to a second plane such that the grid electrode and the
shield electrode come close to the photosensitive drum at a more
downstream side in a rotating direction of the photosensitive drum
than a first plane, wherein the first plane includes the wire
electrode and the rotational axis of the photosensitive drum, and
the second plane is orthogonal to the first plane.
Inventors: |
MATSUURA; Taizo; (Ama-shi,
JP) |
Assignee: |
BROTHER KOGYO KABUSHIKI
KAISHA
Nagoya-shi
JP
|
Family ID: |
45996935 |
Appl. No.: |
13/232007 |
Filed: |
September 14, 2011 |
Current U.S.
Class: |
399/171 |
Current CPC
Class: |
G03G 2215/0141 20130101;
G03G 15/0291 20130101 |
Class at
Publication: |
399/171 |
International
Class: |
G03G 15/02 20060101
G03G015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2010 |
JP |
2010-244232 |
Claims
1. An image forming apparatus comprising: a photosensitive drum
configured to rotate about a rotational axis extending in an axial
direction; and a charger configured to charge the photosensitive
drum, wherein the charger comprises: a wire electrode, which
extends in the axial direction, and to which a voltage for exposing
the photosensitive drum is applied; a grid electrode having a grid
surface that faces the photosensitive drum between the wire
electrode and the photosensitive drum; and a pair of shield
electrodes, which is arranged to face each other with the wire
electrode being interposed therebetween, and which extends in a
substantially orthogonal direction to the grid electrode, and
wherein the grid surface is inclined to a second plane such that
the grid electrode and one of the pair of shield electrodes come
close to the photosensitive drum at a more downstream side in a
rotating direction of the photosensitive drum than a first plane,
wherein the first plane includes the wire electrode and the
rotational axis of the photosensitive drum, and the second plane is
an orthogonal plane to the first plane.
2. The image forming apparatus according to claim 1, further
comprising: an exposure device that is configured to expose the
photosensitive drum; and a developer carrier that is configured to
supply developer to the photosensitive drum, wherein the exposure
device is arranged to face the photosensitive drum between the
developer carrier and the charger.
3. The image forming apparatus according to claim 2, wherein the
exposure device comprises an exposure head that extends in the
axial direction of the photosensitive drum and is arranged adjacent
to a surface of the photosensitive drum.
4. The image forming apparatus according to claim 3, wherein on a
third plane including the rotational axis of the photosensitive
drum and an exposure position on the surface of the photosensitive
drum, which is exposed by the exposure device, a distance between
an extension face of the grid plane and the exposure position is
shorter than a distance between a leading end of the exposure head
and the exposure position.
5. The image forming apparatus according to claim 1, wherein an
angle between the grid surface and the second plane is equal to or
more than 5 degrees.
6. The image forming apparatus according to claim 5, wherein the
angle between the grid surface and the second plane is equal to or
less than 15 degrees.
7. The image forming apparatus according to claim 2, wherein an
angle between the first plane and a third plane including the
rotational axis of the photosensitive drum and an exposure position
on the surface of the photosensitive drum, which is exposed by the
exposure device, is equal to or less than 30 degrees.
8. The image forming apparatus according to claim 1, wherein a
diameter of the photosensitive drum is equal to or less than 18
mm.
9. The image forming apparatus according to claim 8, wherein a
distance between the pair of the shield electrodes is equal to or
more than 7 mm.
10. An image forming apparatus comprising: a photosensitive drum
configured to rotate about a rotational axis extending in an axial
direction; and a charger configured to charge the photosensitive
drum, wherein the charger comprises: a wire electrode that extends
in the axial direction; a grid electrode having a grid surface that
faces the photosensitive drum between the wire electrode and the
photosensitive drum; a first shield electrode, which extends in a
substantially orthogonal direction to the grid electrode, and which
is provided to a downstream side of the wire electrode in a
rotating direction of the photosensitive drum; and a second shield
electrode, which extends in the substantially orthogonal direction
to the grid electrode, and which is provided to an upstream side of
the wire electrode in the rotating direction of the photosensitive
drum, wherein the grid surface is inclined to a second plane that
is orthogonal to a first plane including the wire electrode and the
rotational axis of the photosensitive drum, and wherein a distance
between the first shield electrode and a surface of the
photosensitive drum is shorter than a distance between the second
shield electrode and the surface of the photosensitive drum.
11. The image forming apparatus according to claim 10, further
comprising: an exposure device that is configured to expose the
photosensitive drum; and a developer carrier that is configured to
supply developer to the photosensitive drum, wherein the exposure
device is arranged to face the photosensitive drum between the
developer carrier and the charger.
12. The image forming apparatus according to claim 11, wherein the
exposure device comprises an exposure head that extends in the
axial direction of the photosensitive drum and is arranged adjacent
to a surface of the photosensitive drum.
13. The image forming apparatus according to claim 12, wherein on a
third plane including the rotational axis of the photosensitive
drum and an exposure position on the surface of the photosensitive
drum, which is exposed by the exposure device, a distance between
an extension face of the grid plane and the exposure position is
shorter than a distance between a leading end of the exposure head
and the exposure position.
14. The image forming apparatus according to claim 10, wherein an
angle between the grid surface and the second plane is equal to or
more than 5 degrees.
15. The image forming apparatus according to claim 14, wherein the
angle between the grid surface and the second plane is equal to or
less than 15 degrees.
16. The image forming apparatus according to claim 11, wherein an
angle between the first plane and a third plane including the
rotational axis of the photosensitive drum and an exposure position
on the surface of the photosensitive drum, which is exposed by the
exposure device, is equal to or less than 30 degrees.
17. The image forming apparatus according to claim 10, wherein a
diameter of the photosensitive drum is equal to or less than 18
mm.
18. The image forming apparatus according to claim 17, wherein a
distance between the first shield electrode and the second shield
electrode is equal to or more than 7 mm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Japanese Patent
Application No. 2010-244232 filed on Oct. 29, 2010, the entire
subject matter of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The invention relates to an image forming apparatus having a
charger that charges a photosensitive drum.
BACKGROUND
[0003] There has been proposed a related-art image forming
apparatus that includes a charger having a discharge wire (wire
electrode) and a grid electrode and generating the corona discharge
from the wire electrode in order to charge a surface of a
photosensitive drum. In the related-art image forming apparatus,
the charger is arranged such that the grid electrode (grid surface
opposed to the photosensitive drum) is orthogonal to a plane
including the wire electrode and a rotational center portion of the
photosensitive drum.
SUMMARY
[0004] Illustrative aspects of the invention provide an image
forming apparatus capable of reducing a size thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a view showing an overall configuration of a color
printer according to an exemplary embodiment of the invention;
[0006] FIG. 2 is an enlarged view showing a configuration around a
photosensitive drum; and
[0007] FIGS. 3A-3B illustrate effects of the invention, where FIG.
3A shows a configuration of a comparative example in which a grid
surface is arranged in parallel with an orthogonal plane and FIG.
3B shows a configuration of an exemplary embodiment in which the
grid surface is inclined to the orthogonal plane.
DETAILED DESCRIPTION
General Overview
[0008] In recent years, as a size of the image forming apparatus is
reduced, a diameter of the photosensitive drum is also made to be
smaller. However, since the photosensitive drum has, on a
circumferential surface thereof, an exposure position to be exposed
by an exposure device and the charger, a developing roller, a
transfer roller, a cleaning roller and the like are arranged around
the photosensitive drum, gaps therebetween are reduced as the
diameter of the photosensitive drum is made to be smaller.
Specifically, since there is a limit to the miniaturization of the
charger, there is also a limit to the miniaturization of the
photosensitive drum (reducing a size of the image forming
apparatus).
[0009] Therefore, illustrative aspects of the invention provide an
image forming apparatus capable of reducing a size thereof.
[0010] According to illustrative aspects of the invention, there is
provided an image forming apparatus comprising: a photosensitive
drum configured to rotate about a rotational axis extending in an
axial direction; and a charger configured to charge the
photosensitive drum, wherein the charger comprises: a wire
electrode, which extends in the axial direction, and to which a
voltage for exposing the photosensitive drum is applied; a grid
electrode having a grid surface that faces the photosensitive drum
between the wire electrode and the photosensitive drum; and a pair
of shield electrodes, which is arranged to face each other with the
wire electrode being interposed therebetween, and which extends in
a substantially orthogonal direction to the grid electrode, and
wherein the grid surface is inclined to a second plane such that
the grid electrode and one of the pair of shield electrodes come
close to the photosensitive drum at a more downstream side in a
rotating direction of the photosensitive drum than a first plane,
wherein the first plane includes the wire electrode and the
rotational axis of the photosensitive drum, and the second plane is
an orthogonal plane to the first plane.
[0011] According to the image forming apparatus configured as
described above, the grid surface is inclined to the orthogonal
plane of the plane including the wire electrode and the rotational
center portion of the photosensitive drum such that the grid
electrode and the shield electrode come close to the photosensitive
drum at the more downstream side in the rotating direction of the
photosensitive drum than the plane including the wire electrode and
the rotational center portion of the photosensitive drum.
Accordingly, an end portion, which faces the photosensitive drum,
of the shield electrode of the charger, which shield electrode is
positioned at the downstream side in the rotating direction of the
photosensitive drum, can be made to be distant from an optical axis
of the exposing light. Thereby, it is possible to secure a space
between the charger and the optical axis of the exposing light, and
thus it is possible to closely arrange the charger to the optical
axis so as to make a diameter of the photosensitive drum smaller.
As a result, the size of the image forming apparatus can be further
reduced.
[0012] In addition, the grid electrode is inclined such that the
downstream side thereof in the rotating direction of the
photosensitive drum is more close to the photosensitive drum than
the plane including the wire electrode and the rotational center
portion of the photosensitive drum. Accordingly, a distance between
the surface of the photosensitive drum and the grid electrode (grid
surface) is narrower at the downstream side in the rotating
direction of the photosensitive drum and is wider at the upstream
side in the rotating direction. Therefore, it is possible to reduce
an amount of ions (ionized air by the corona discharge) flowing
toward the downstream side (toward the exposure position) in the
rotating direction of the photosensitive drum. According thereto,
it is possible to suppress the surface of the photosensitive drum
from being re-charged after the exposure. As a result, it is
possible to form a favorable image.
[0013] According to the invention, the grid electrode is inclined
to the orthogonal plane to the plane including the wire electrode
and the rotational center portion of the photosensitive drum so
that the grid electrode and the shield electrode come close to the
photosensitive drum at the downstream side in the rotating
direction of the photosensitive drum. Accordingly, it is possible
to make the diameter of the photosensitive drum smaller, so that it
is possible to further reduce the size of the image forming
apparatus.
Exemplary Embodiments
[0014] Hereinafter, exemplary embodiments of the invention will now
be described with reference to the drawings. In the following
descriptions, a configuration of an image forming apparatus 1 will
be briefly described and then the characteristics of the invention
will be described. Incidentally, a color printer is one example of
the image forming apparatus 1.
[0015] Also, in the following descriptions, the directions are
described on the basis of a user who uses the image forming
apparatus 1. That is, the left side of FIG. 1 is referred to as the
`front side`, the right side is referred to as the `rear side`, the
front side is referred to as the `right side` and the inner side is
referred to as the `left side.` Also, the upper-lower direction of
FIG. 1 are referred to as the `upper-lower` direction.
[0016] (Overall Configuration of Image Forming Apparatus)
[0017] As shown in FIG. 1, the image forming apparatus 1 includes,
in a body casing 10, a feeder unit 20 that feeds sheets S, an image
forming unit 30 that forms an image on the fed sheet S and a sheet
discharge unit 90 that discharges the sheet S having an image
formed thereon.
[0018] An upper cover 12 is provided to an upper side of the body
casing 10. The upper cover 12 is configured to be rotatable (opened
and closed) about the rear side serving as a support point. A sheet
discharge tray 13, on which the sheet S discharged from the body
casing 10 is put, is provided on an upper surface of the upper
cover 12. Four holding members 40 that hold LED units 40 are
provided on a lower surface of the upper cover.
[0019] The feeder unit 20 is provided at the lower part in the body
casing 20. The feeder unit 20 includes a feeder tray 21, which
receives therein the sheets S, and a sheet feeding mechanism 22,
which feeds the sheet S from the feeder tray 21 to the image
forming unit 30. The sheets S in the feeder tray 21 are separated
one at a time by the sheet feeding mechanism 22 and are then
supplied to the image forming unit 30.
[0020] The image forming unit 30 includes four LED units 40 that
are an example of an exposure device, four process units 50, a
transfer unit 70 and a fixing unit 80.
[0021] The LED unit 40 is opposed to the upper part of a
photosensitive drum 52 at a closed state of the upper cover 12. The
LED unit 40 is configured to expose a surface of the photosensitive
drum 52. The LED unit 40 is held at the upper cover 12 by the
holding member 14, so that the LED unit 40 is spaced from the
photosensitive drum 52 as the upper cover 12 is opened. The LED
unit 40 will be specifically described later.
[0022] The process units 50 are arranged in parallel with each
other in the front-rear direction between the upper cover 12 and
the feeder unit 20. The process units 50 are detachably mounted to
the body casing 10 at an opened state of the upper cover 12. The
process unit 50 includes a process frame 51, the photosensitive
drum 52, a charger 100, a developing device 54 and a cleaning
roller 55.
[0023] The process frame 51 rotatably supports the photosensitive
drum 52 and the cleaning roller 55. Further, the process frame 51
supports a wire electrode 110, a grid electrode 120 and shield
electrodes 131, 132 of the charger 100, which will be described
later.
[0024] The photosensitive drum 52 has a photosensitive layer formed
on a surface (outer peripheral surface) of a cylindrical drum body
having conductivity. The photosensitive drum 52 is configured to
rotate in a counterclockwise direction (arrow direction) of FIG.
1.
[0025] The charger 100 is a scorotron-type charger that charges the
surface of the photosensitive drum 52. The charger 100 is arranged
obliquely upper-rear side of the photosensitive drum 52 and faces
the photosensitive drum 52.
[0026] The developing device 54 is detachably mounted to the
process frame 51. The developing device 54 is arranged obliquely
upwards to the front of the photosensitive drum 52 at the mounted
state to the process frame 51. The developing device 54 includes a
developing roller 54A that is an example of a developer carrier to
supply toner (developer) to the photosensitive drum 52, a supply
roller 54B, a layer thickness regulation blade 54C and a toner
accommodating part 54D that accommodates the toner therein.
[0027] The cleaning roller 55 collects foreign substances such as
paper dusts and dusts adhered on the surface of the photosensitive
drum 52, the toner remained on the surface of the photosensitive
drum 52 and the like. The cleaning roller 55 is arranged to contact
the rear part of the photosensitive drum 52.
[0028] The transfer unit 70 is provided between the feeder unit 20
and the process unit 50. The transfer unit 70 includes a driving
roller 71, a driven roller 72 and an endless conveyance belt 73
extending between the driving roller 71 and the driven roller 72.
The conveyance belt 73 contacts an outer surface of the respective
photosensitive drums. At the inner side of the conveyance belt, the
respective transfer rollers 74 are arranged to interpose the
conveyance belt 73 between the respective transfer rollers and the
respective photosensitive drums 52. The fixing unit 80 is provided
at the rear part of the process unit 50 and the transfer unit 70.
The fixing unit 80 includes a heating roller 81 and a pressing
roller 82, which is opposed to the heating roller 81 and presses
the heating roller 81.
[0029] In the image forming unit 30, the surface of the
photosensitive drum 52 is uniformly charged by the charger 100 and
is then exposed by the LED unit 40, so that an electrostatic latent
image is formed on the photosensitive drum 52 based on image data.
In addition, the toner in the toner accommodating part 54D is
supplied to the developing roller 54A through the supply roller
54B, is introduced between the developing roller 54A and the layer
thickness regulation blade 54C and is then carried on the
developing roller 54A as a thin layer having a predetermined
thickness.
[0030] The toner carried on the developing roller 54A is supplied
to the photosensitive drum 52, so that the electrostatic latent
image is visualized and a toner image is thus formed on the
photosensitive drum 52. After that, as the sheet S fed from the
feeder unit 20 is conveyed between the photosensitive drums 52 and
the conveyance belt 73 (transfer rollers 74), the toner images
formed on the respective photosensitive drums 52 are sequentially
overlapped and transferred on the sheet S. The sheet S, to which
the toner images are transferred, is conveyed between the heating
roller 81 and the pressing roller 82, so that the toner images are
heated and fixed.
[0031] The sheet discharge unit 90 includes a sheet discharge path
91, which guides the sheet S conveyed from the fixing unit 80, and
a plurality of conveyance rollers 92 that conveys the sheet S. The
sheet S, to which the toner images are heated and fixed, is
conveyed through the sheet discharge path 91 by the conveyance
rollers 92 and is discharged to the outside of the body casing 10
so as to be put on the sheet discharge tray 13.
[0032] (Configuration Around Photosensitive Drum)
[0033] In the followings, detailed configuration around the
photosensitive drum 52 will be described, based on the
configuration and arrangement of the LED unit 40 and the charger
100.
[0034] As shown in FIG. 2, the LED unit 40 includes an LED head 41,
which is an example of an exposure head, and a support frame 42.
The LED unit 40, more specifically, the LED head 41 is arranged to
face the surface of the photosensitive drum 52 between the
developing roller 54A (developing device 54) and the charger
100.
[0035] The LED head 41 extends in the left-right direction (axial
direction of the photosensitive drum 52). A lower end (leading end)
of the LED head 41 is arranged adjacent to the surface of the
photosensitive drum 52 at the closed state of the upper cover 12. A
plurality of light emitting parts (LEDs) (not shown) is arranged at
the leading end of the LED head 41 in the left-right direction. In
the invention, the light emitting parts may be linearly arranged or
zigzag-arranged in the left-right direction. In addition, the row
of the light emitting parts may be one or two or more rows of the
light emitting parts may be provided side by side in the front-rear
direction. The support frame 42 supports the LED head 41 to the
upper cover 12. An upper part of the support frame 42 is mounted to
the upper cover 12 through the holding member 14 while a lower part
thereof supports the LED unit 41.
[0036] The LED unit 40 turns on and off the light emitting parts on
the basis of the image data so as to expose the surface of the
charged photosensitive drum 52. In the following descriptions, a
part of the surface of the photosensitive drum 52, which is exposed
by the LED unit 40, is referred to as an exposure position PE. In
this exemplary embodiment, an intersection point (intersection
line) of the surface of the photosensitive drum 52 and an optical
axis of the exposing light emitted from the LED head 41, when seen
from the left-right direction, is the exposure position PE.
[0037] Incidentally, when the light emitting parts of the LED head
41 are zigzag-arranged or two or more rows of the light emitting
parts are arranged side by side, a plurality of optical axes is
formed when seen from the left-right direction. In this case,
regarding the circumferential direction of the photosensitive drum
52, a middle position between an intersection of the surface of the
photosensitive drum 52 and the optical axis at the most upstream
side in the rotating direction of the photosensitive drum 52 and an
intersection of the surface of the photosensitive drum 52 and the
optical axis at the most downstream side in the rotating direction
is the exposure position.
[0038] The charger 100 includes the wire electrode 110, the grid
electrode 120 and a pair of shield electrodes 131, 132. The charger
100 is arranged obliquely upper-rear side of the photosensitive
drum 52 and faces the photosensitive drum 52 at a predetermined
distance from the surface of the photosensitive drum 52.
[0039] The wire electrode 110 is a metal wire that generates the
corona discharge as a voltage for exposing the photosensitive drum
52 is applied. The wire electrode 110 is installed in parallel with
the rotational axis (rotational center portion C) of the
photosensitive drum 52 and extends in the left-right direction
between the pair of shield electrodes 131, 132.
[0040] The grid electrode 120 is a metal plate member that is set
with a potential (including zero potential) different from that of
the wire electrode 110 so as to control an amount of ions reaching
the surface of the photosensitive drum 52. The grid electrode 120
has a planar grid surface 121 that is opposed to the photosensitive
drum 52 between the wire electrode 110 and the photosensitive drum
52. The grid surface 121 extends in the left-right direction. The
grid surface 121 includes a plurality of grid holes 122 for
enabling the ions generated by the corona discharge of the wire
electrode 110 to pass therethrough.
[0041] The shield electrodes 131, 132 are metal plate members that
are arranged to face each other with the wire electrode 110 being
interposed therebetween, when seen from the left-right direction,
and extend in a substantially orthogonal direction to the grid
electrode 120 (grid surface 121). The shield electrodes 131, 132
have the substantially long plate shapes extending along the
rotational center portion C (the left-right direction) of the
photosensitive drum 52 and are arranged in parallel with each
other. Incidentally, in this exemplary embodiment, the shield
electrodes 131, 132 are integrated with the grid electrode 120.
However, the invention is not limited thereto. For example, the
shield electrodes may be parts different from the grid electrode
120.
[0042] In the following descriptions, one of the shield electrodes
131, 132, which is arranged at the downstream side (front side) of
the photosensitive drum 52 in the rotating direction, is referred
to as a front-side shield electrode 131, and another one of the
shield electrodes 131, 132, which is arranged at the upstream side
(back side) in the rotating direction, is referred to as a
back-side shield electrode 132.
[0043] In this exemplary embodiment, the charger 100, more
specifically, the grid surface 121 is inclined to an orthogonal
plane PL2 of a plane PL1 including the wire electrode 110 and the
rotational center portion C of the photosensitive drum 52 so that
the grid electrode 120 and the front-side shield electrode 131 are
close to the photosensitive drum 52 at a front side than the plane
PL1.
[0044] The charger 100 is arranged as described above. Thereby, the
configuration of this exemplary embodiment shown in FIG. 3B enables
a lower end portion 133 of the front-side shield electrode 131 to
be more distant from the LED unit 40 (optical axis of the exposing
light (refer to a plane PL3)), compared to a configuration shown in
FIG. 3A in which a grid surface 121' of a charger 100' is arranged
along the orthogonal plane PL2. According to this configuration, it
is possible to secure a space between the charger 100 and the LED
unit 40, and thus it is possible to closely arrange the charger 100
and the LED unit 40, as shown in FIG. 3B. Therefore, it is possible
to make a diameter of the photosensitive drum 52 smaller, so that
it is possible to further reduce the size of the image forming
apparatus 1.
[0045] Incidentally, as shown in FIG. 2, an angle .theta.1 between
the grid surface 121 and the orthogonal plane PL2 is preferably
equal to or more than 5 degrees and equal to or less than 15
degrees. According to this configuration, it is possible to
favorably charge the surface of the photosensitive drum 52 while
inclining the charger 100 (grid surface 121).
[0046] In addition, an angle .theta.2 between the plane PL1 and the
plane PL3 including the rotational center portion C of the
photosensitive drum 52 and the exposure position PE is preferably
equal to or less than 30 degrees. According to this configuration,
since the charger 100 and the LED unit 40 come closer to each
other, it is possible to make the diameter of the photosensitive
drum 52 much smaller. As a result, it is possible to further reduce
the size of the image forming apparatus 1.
[0047] Furthermore, the diameter D1 of the photosensitive drum 52
is preferably equal to or less than 18 mm. At this time, a distance
D2 between the shield electrodes 131, 132 is preferably equal to or
more than 7 mm. According to this configuration, since the spark
can be prevented from being occurred, it is possible to stabilize
the corona discharge.
[0048] In this exemplary embodiment, the grid electrode 120 is
inclined so that the front side thereof than the plane PL1 is close
to the photosensitive drum 52. Accordingly, a distance between the
surface of the photosensitive drum 52 and the grid surface 121 is
narrower at the front side than the plane PL1 and is wider at the
back side than the plane PL1. Therefore, the configuration of this
exemplary embodiment shown in FIG. 3B can reduce the amount of ions
flowing toward the LED head 41 (refer to the arrows), compared to
the configuration shown in FIG. 3A. Thereby, it is possible to
suppress the surface of the photosensitive drum 52 from being
re-charged after the exposure. Hence, it is possible to make a
difference of potentials of the exposed part and the non-exposed
part greater, so that it is possible to form a favorable image.
[0049] The invention configured as described above is particularly
useful in the configuration in which the exposure device is
arranged to face the photosensitive drum 52 between the developing
roller 54A and the charger 100, as the image forming apparatus 1.
That is, according to such configuration, it is not easy to make
the diameter of the photosensitive drum 52 smaller, compared to a
configuration in which the laser light is illuminated from an
exposure device arranged above a plurality of process units to
expose the photosensitive drums. Accordingly, by applying the
invention to the image forming apparatus having the configuration
such as the image forming apparatus 1, it is possible to make the
diameter of the photosensitive drum smaller and to thus further
reduce the size of the image forming apparatus 1.
[0050] Although the exemplary embodiment of the invention has been
described, the invention is not limited thereto. The specific
configuration can be appropriately changed without departing from
the scope of the invention.
[0051] In the above-described exemplary embodiment, the front-side
shield electrode 131 faces the LED unit 40. However, the invention
is not limited thereto. For example, a frame wall of the charger
100 supporting the shield electrodes 131, 132 and the grid
electrode 120 may be provided between the front-side shield
electrode 131 and the LED unit 40. Incidentally, when the invention
is applied to such a configuration, the frame wall is also inclined
to the orthogonal plane PL2 together with the shield electrodes
131, 132 and the grid electrode 120.
[0052] In the above-described exemplary embodiment, in the process
unit 50, the developing device 54 (developing roller 54A) is
detachably mounted to the photosensitive drum 52. However, the
invention is not limited thereto. For example, the process unit may
have a configuration in which the photosensitive drum and the
developing roller (developer carrier) are integrated (i.e., the
detachable mounting is impossible).
[0053] In the above-described exemplary embodiment, the LED head 41
having the plurality of LEDs (light emitting parts) arranged
thereto has been exemplified as the exposure head that is arranged
adjacent to the surface of the photosensitive drum 52. However, the
invention is not limited thereto. For example, an EL device, a
fluorescent member and the like may be adopted as the light
emitting part. In addition, the exposure head may be configured so
that an optical shutter such as liquid crystal device, PLZT device
and the like is arranged at an output side of a backlight such as
fluorescent lamp, LED and the like.
[0054] In the above-described exemplary embodiment, the LED unit 40
has been exemplified as the exposure device that is arranged to
face the photosensitive drum 52 between the developing roller 54A
(developer carrier) and the charger 100. However, the invention is
not limited thereto. For example, the exposure device that is
arranged to face the photosensitive drum between the developer
carrier and the charger may be a laser scanner that is provided in
correspondence to each photosensitive drum and scans the laser
light on the surface of the photosensitive drum at high speed and
thus exposes the surface of the photosensitive drum after the
charge.
[0055] In addition, the exposure device is not limited to the
configuration in which it is arranged to face the photosensitive
drum between the developer carrier and the charger. For example,
one exposure device (laser scanner and the like) may be arranged
above the plurality of processing units (photosensitive drums).
[0056] The image forming apparatus 1 may not be limited to the
color printer. For example, the image forming apparatus 1 may be a
printer that forms a black-white image. Alternatively, the image
forming apparatus 1 may be a copier or multi-function device.
* * * * *